Energy generation and storage has long been a subject of study and development. Of special import is the storage of energy in a compact form that can be easily charged and discharged, such as rechargeable batteries and/or capacitors. The components of these various systems have been generally optimized by seeking to achieve the maximum stored energy density. However, most, if not all, commercially-available systems yield far less than their theoretical energy density. One such energy storage system utilizes activated carbon electrodes to store ions therein, and which, upon discharge, releases the ions to generate an electrical current. One example of an activated carbon electrode system is a double layer capacitor system described in U.S. Pat. No. 3,536,963. The mechanism for energy storage is based on the formation of an electrical double layer at the interface between an activated carbon electrode and a supporting electrolyte under an applied electrical field. Double layer capacitors will accept and store significant amounts of energy at a wide variety of potentials, unlike batteries where a given threshold voltage must be exceeded. Optimization of this type of system is based upon enhancing the charge storage capacity of the activated carbon electrode. Double layer capacitors can exhibit a capacity equivalent to tens of farads per gram of activated carbon when the activated carbon has a surface area in excess of 1000 square meters per gram (m.sup.2 /g). However, even this improvement has limited application because the energy density needs to be even greater. One way of improving the charge storage capacity is to coat the surface of the activated carbon with a material. U.S. Pat. No. 4,633,372, incorporated herein by reference, modifies the activated carbon with a polyoxometalate in order to provide a reversible electron transfer between the electrolyte and the electrode. These iso- and hetro-polyions, the example, the polyoxometalates, are known to exhibit reversible multi-electron transferring reaction, and are used to modify the carbon electrodes to increase the charge storage capacity. However, this modification does not increase the capacity significantly, since the absorption of the polyoxometalates only forms a monolayer on the surface of the carbon, and the polyoxometalate can be easily leached away during long term cycling of the electrode. In addition, the prior art methods require very long processing times (2-3 weeks) to get the polyoxometalate properly coated onto the surface of the carbon.
Clearly, it would be desirable to form an electrode that exhibits increased charge storage capacity, thus further enabling miniaturization of energy storage devices.